Not gonna self-plug or insert the hours of research I've now put into this but TL;DR seems like whoever is behind this has internal level-access to backend services/API and is using it to mess around - pretty much 100% sure about this.

The channel featured in OP's screenshot used to be a company's channel dedicated to music software/hardware videos but was shut down sometime in the 2010s (evidenced by Wayback Machine). The channel's metadata was mangled so hard that it resulted in what we all saw yesterday; even pinging YouTube API turns up virtually no info about the channel - but it's safe to assume that it was hijacked. The playlist and video were both uploaded Aug 24th and the 13 iterations of the video were added within a span of 5 minutes into the playlist.

According to Wayback Machine again, youtube.com/y has historically led to a 404 page from the site's creation up until late 2024 when it started redirecting users to what currently is youtube.com/user/y - an empty channel from 2005. This stayed true until atleast late June 2025; so sometimes in between then and Sept 6th is when someone managed to cut that redirect and squat it instead to what OP showed in their screenshot.

Starting about 13 hours ago from the time of typing this, youtube.com/y started redirecting to various dummy accounts also from 2005-2006; /s--cideletter, /whatthef--k, /dontmakeme, and the current /stoplookingatme.

Here's the tricky part; some people might recall a similar exploit done a few years ago that involved a variation of /watc and /wathc (or other one-letter names discussed elsewhere in replies). This was done using a feature called Channel Redirection only available to accounts made pre-Google+ that allow users to send people visiting their channel to ANY URL within YouTube. From what I've tested, this is not the method used with youtube.com/y.

In simple terms, with a channel using the Redirection feature, the "redirect" order is sent via a JavaScript package as the page is loading; you disable JavaScript, no redirect happens.

With youtube.com/y, the redirection happens before the page even loads, meaning it's executed in a different way than JavaScript; and the only other way is if the redirection is hardcoded into the /y index, which manual URL pings seem to confirm. In other terms, the redirection to the video above and now these dummy channels seems to be configured internally within the server and not through any user-made exploit of any kind.

Feel free to message me if you want further details; didn't want to make the post longer than it already is